haskell新手这个CLI bmiTell函数有什么问题？

Question

我得到了parse error的跟踪bmiTell为什么？

Prelude> :{
Prelude| let  bmiTell :: Double -> Double -> String
Prelude| bmiTell weight height
Prelude|   weight / height ^ 2 <= 18.5 = "You're underweight, you emo, you!"
Prelude|   weight / height ^ 2 <= 25.0 = "You're supposedly normal. Pffft, I bet you're ugly!"
Prelude|   weight / height ^ 2 <= 30.0 = "You're fat! Lose some weight, fatty!"
Prelude|   otherwise = "You're a whale, congratulations!"
Prelude| :}

<interactive>:19:1: parse error on input `bmiTell'

Answer 1

您的缩进正在抛出解析器。看一看这个：

Prelude> :{
Prelude| let bmiTell :: Double -> Double -> String
Prelude| bmiTell weight height = undefined
Prelude| :}

<interactive>:6:1: parse error on input `bmiTell'
Prelude> :{
Prelude| let bmiTell :: Double -> Double -> String
Prelude|     bmiTell weight height = undefined
Prelude| :}
Prelude>

Answer 2

您正在尝试在函数定义中使用卫兵，因此

weight / height ^ 2 

应该是

| weight / height ^ 2 

其他的也是相似的。

正如@DiegoNolan在注释中指出的那样，您确实应该将这个定义放在源文件中并加载到ghci中。